Effect of Friction on Finite Element Contact and Wear Predictions of Metal-on-Plastic Hip Replacements

Finite Element wear predictive modelling is a powerful tool that can replace or support costly and time-consuming wear tests. Despite the lively research in this field, particularly in applications to hip replacements, some issues are still open, such as the role of friction in numerical simulations. Indeed, in most wear models, frictionless contact conditions are assumed and wear routines are independent from f. However, the effect of friction on contact and wear modelling of metal-on-plastic hip replacements has never been fully explored in the literature. In this study we analyse how the friction coefficient affects both the contact features (nominal contact point trajectory, components of the contact force and contact pressure) and the wear parameters, (wear volume and linear wear distribution). A case study of a 32 mm implant was simulated under two different loading and kinematic conditions, considering both vertical and 3D load, and varying the friction coefficient f within the range 0–0.3, for a given k value. Results show that a frictional contact has longer and wider trajectories of the nominal contact point, but slightly lower normal force and contact pressure values, with respect to a frictionless solution. Consequently, contact pressure maps are shifted with respect to the frictionless case but values remain almost the same changing f. The wear volume slightly decreases with f whilst wear maps are very sensitive to it. Results suggest that for f ≤ 0.1 the frictionless hypothesis can be adopted achieving accurate results with the advantage of reduced computational costs.